If you keep your mod source in version control, it may have some merge tools. If you don’t keep it in version control, you should.
I use subversion: http://subversion.tigris.org/ and http://tortoisesvn.tigris.org/
The latter has a GUI diff/merge tool.
Note that even if you didn’t keep your source in version control to start with, you can still use it to show you exactly where your changes are.
- unpack the original SDK, check it in, tag it.
- copy your source into that tree, check it in, tag it.
- copy the 2.6 update in, merge as required, check it in.
If you want to get fancy (and be able to see the differences between 2.56 and 2.6 at a glance) make a branch for 2.6 instead, and then merge that into your modified tree. Of course, if you weren’t an SCM engineer in past life, the above may not make any sense :moo:
But really, using some kind of SCM software is a very good idea, even if you only work alone. Being able to see changes and between versions, and revert without having to worry about manually copying files and having all kinds of different trees will save you loads of work in the long run.